1. Field of the Invention
The present invention relates to a pharmaceutical composition for treating cancer, comprising sorafenib and GW5074. The invention also discloses a method for dissociating a protein complex consisting of c-Raf and DAPK by drugs, which can then be used as targets for designing new drugs. Additionally, the invention further provides a method for screening drugs utilizing proteins c-Raf and DAPK as well as the phosphorylation status of DAPK.
2. Description of the Prior Art
Activation of the proto-oncogenes or deficiency of the tumor suppressor genes often leads to cancer cell development. Ras is a proto-oncogene and activation of Ras protein is normally triggered by receptor tyrosine kinase (TKIs) on the cell membrane. Activated Ras protein binds with RAF and subsequently transmits the signal downstream to activate the MAPK pathway which, in turn, regulates cell growth as well as cell differentiation. Activated Grb-sos protein arising from binding of a growth factor to its receptor on the cell membrane leads to phosphorylation of downstream Ras-GDP protein, and the resulting Ras-GTP then binds to the N-terminus of Raf protein and activates Raf, which further regulates the activation of ERK through phosphorylation of MEK. Next, activated ERK enters the cell nucleus and induces cancer cell proliferation. Therefore, countless drugs that are designed specifically against these proto-oncogenes such as these tyrosine kinase inhibitors (TKIs) were generated, only to discover that many cancer patients developed drug resistance during the treatment. Consequently, combination therapy that specifically targets the signaling transduction pathway of tyrosine kinase has become a common treatment method.
Angiogenesis as well as cell proliferation play essential roles in tumor growth. Binding of vascular endothelial growth factor (VEGF-A) released from cancer cells in vast amounts to vascular endothelial growth factor receptor (VEGFR-2) on the surface of the endothelial cells of a tumor activates the signaling transduction pathway of Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) which in turn induces angiogenesis of endothelial cells. Meanwhile, the Ras-ERK pathway also facilitates cancer cell proliferation. In addition, loss of regulation of the Ras-Raf-ERK pathway has been shown in a number of tumor cell lines. Thus, VEGF and Raf may be the best targets for inhibition of tumor growth.
Sorafenib (Nexavar®, BAY 43-9006, Bayer HealthCare Pharmaceuticals) is an oral Multi-Kinase Inhibitor commonly used for treating various cancers. Sorafenib can inhibit proteins such as Raf, VEGF receptor, platelet-derived growth factor (PDGF) receptor, KIT and Fms-like tyrosine kinase-3 (FLT-3). A number of studies have indicated that sorafenib inhibits tumor growth by inhibiting Raf signaling pathway in different cancer cells while suppressing proliferation of the endothelia cells surrounding cancer cells through inhibition of VEGF as well as PDGF signaling pathways, and subsequently induces cancer cell death. The design and test results of these drugs are ideal. However, after few years of clinical applications, it was unfortunate discovered that, although the tumor size at the early stage of treatment was efficiently inhibited by sorafenib, the drug not only cannot eradicate the tumor completely, but causes serious side effects. Moreover, these treated cancer cells developed drug resistance after prolonged treatment. Additionally, in recent years, certain studies have shown that inhibition of Raf signaling pathway in cancer cells leads to reduced inhibition of sorafenib due to alternative regulation by different molecules in cancer cells. Most importantly, some evidence further indicated that the inhibition effects of sorafenib on cancer cells may not be regulated by the Raf pathway. Hence, the aforementioned imperfections need to be further improved.